Anesthetic delivery system

Abstract

An anesthetic delivery system for use in conjunction with an anesthetic return system for reutilizing anesthetic exhaled by a subject, the system including a measurement system operatively connected to a breathing circuit for continuously measuring at least one flow parameter and anesthetic content of a gas stream reaching the subject and a control system for receiving input from the measurement system and controlling the amount of anesthetic entering the system, the control system including an input device for inputting a setting that corresponds to a desired amount of anesthetic in the gas stream reaching the subject, and utilizing a control algorithm for controlling the amount of anesthetic entering the system based on said desired amount of anesthetic, and flow and anesthetic content parameters as determined by the measurement system, such that the control algorithm is adapted to supplement anesthetic already in gas stream flowing to the subject to attain a level of anesthetic reaching the subject that correspond to the desired amount set via the input device.

1 .- 37 . (canceled) 
     
     
         38 . An anesthetic delivery system ( 10 ) for use in conjunction with a ventilator ( 12 ), and a breathing circuit ( 16 ), the breathing circuit ( 16 ) organizing gas flow in relation to a subject and operatively connected to an anesthetic return system ( 19   e ,  70 ) for re-utilizing anesthetic exhaled by the subject and including an inspiratory limb ( 19   i ) for directing a gas stream from the ventilator ( 12 ) towards the subject, the system comprising:
 an anesthetic delivery device ( 20 ) operable for introducing a variable amount of anesthetic into the breathing circuit in a vaporized form;   a homogenizer ( 39 ) having an anesthetic inlet port and configured for distributing the anesthetic in vaporized form into the gas stream flowing towards the subject, the homogenizer receiving into the anesthetic inlet port the anesthetic in vaporized form directed by the breathing circuit from the anesthetic delivery device, such that anesthetic vapor is received in the inspiratory limb ( 19   i ) in a portion of the gas stream passing through the homogenizer, the homogenizer ( 39 ) configured to be fluidly connected to the inspiratory limb ( 19   i ) of the breathing circuit ( 16 ) such that anesthetic vapor that enters the homogenizer ( 39 ) during exhalation is stored in the homogenizer ( 39 ) during exhalation and is distributed in the gas stream directed towards the subject, via the inspiratory limb ( 19   i ), during inhalation;   a measurement system configured to be operatively connected to the breathing circuit for continuously measuring flow and anesthetic content of the gas stream, the measurement system comprising an anesthetic analyzer ( 46 ) for analyzing a concentration of anesthetic in the gas stream flowing towards the subject including anesthetic returned via the anesthetic return system, and a flow sensor ( 44 ) for determining a rate of flow of the gas stream to the subject;   a control system for receiving input from the measurement system and controlling the amount of anesthetic entering the inlet port from the anesthetic delivery device, the control system operatively associated with an input device for inputting a setting that corresponds to a desired amount of anesthetic in the gas stream reaching the subject, the input device configured for setting the desired amount of anesthetic in terms of a selectable concentration of anesthetic in the gas stream reaching the subject;   the control system ( 45 ) operable to execute a control algorithm that controls the amount of anesthetic entering the anesthetic inlet port based on the setting, and based on the rate of flow of the gas stream flowing to the subject and the concentration of anesthetic in the gas stream, as determined by the measurement system, such that anesthetic already in the gas stream flowing to the subject is supplemented to attain a level of anesthetic reaching the subject that corresponds to the setting.   
     
     
         39 . An anesthetic delivery system according to  claim 38 , wherein the breathing circuit includes a carbon dioxide scrubber and an expiratory limb for receiving gas exhaled by the subject, the expiratory limb and the carbon dioxide scrubber fluidly connected to the inspiratory limb such that the gas stream flowing to the subject via the inspiratory limb includes exhaled gas containing anesthetic gas exhaled by the subject. 
     
     
         40 . An anesthetic delivery system according to  claim 38 , wherein the control algorithm:
 (a) outputs a value corresponding to a volume of gas inspired in each of a series of respective breaths [i] using input from the measurement system; and   (b) uses the volume of each such respective breath [i] and its pre-top up anesthetic content to compute the amount of anesthetic set to enter the anesthetic inlet port to attain the desired amount of anesthetic in the gas stream reaching the subject.   
     
     
         41 . An anesthetic delivery system according to  claim 38 , wherein the control algorithm:
 (a) outputs a value corresponding to a volume of gas inspired measured for each of a series of consecutive time intervals [t] using input from the measurement system; and   (b) uses a respective volume of gas measured for a respective time interval [t] and its pre-top up anesthetic content to compute the amount of anesthetic required to attain the desired amount of anesthetic in the gas stream reaching the subject;   where the control system is programmed to top-up the anesthetic already in the gas stream within a next ensuing time interval [t+1] or a plurality of next ensuing time intervals, as required, to attain the desired amount of anesthetic in the gas stream reaching the subject.   
     
     
         42 . An anesthetic delivery system according to  claim 40 , wherein the control system is programmed to send a control signal to the anesthetic delivery device to signal the anesthetic delivery device to deliver an amount of anesthetic corresponding to difference between the desired amount of anesthetic and the amount of anesthetic already in the gas steam from the anesthetic return system in a respective breath [i], in a subsequent breath [i+1], any requisite addition of anesthetic to attain or maintain the selected concentration of anesthetic in the gas stream delivered to the anesthetic inlet port, added in increments computed on a breath by breath basis, one breath behind. 
     
     
         43 . An anesthetic delivery system according to  claim 38 , wherein the anesthetic delivery device is a vaporizer which comprises:
 a reservoir containing liquid anesthetic;   a vaporization chamber, to convert the liquid anesthetic into gaseous anesthetic;   a liquid pump for transferring liquid anesthetic from the reservoir to the vaporization chamber, the liquid pump being adapted to transfer anesthetic to the vaporization chamber at an adjustable flow rate controlled by the control system; and   a gas pump, to transfer the gaseous anesthetic from the vaporization chamber to the anesthetic inlet port.   
     
     
         44 . An anesthetic delivery system according to  claim 38 , wherein the breathing circuit includes a reflector, and a separate expiratory limb for receiving gas exhaled by the subject, the reflector operatively connected to the expiratory limb for reversibly trapping or adsorbing anesthetic in gas exhaled by the subject and between the inspiratory limb and the ventilator, wherein the ventilator drives inspiratory gas through the reflector into the inspiratory limb such that the gas stream flowing to the subject via the inspiratory limb includes anesthetic gas trapped by the reflector. 
     
     
         45 . An anesthetic delivery system according to  claim 44 , wherein the reflector is positioned in the breathing circuit between the inlet port and the ventilator. 
     
     
         46 . An anesthetic delivery system according to  claim 44 , wherein the reflector is positioned in the breathing circuit between the measurement system and the ventilator and wherein the control system is programmed to top-up the anesthetic returned to the inspiratory limb from the reflector. 
     
     
         47 . An anesthetic delivery system according to  claim 44 , wherein the reflector is positioned in the breathing circuit between the homogenizer and the ventilator. 
     
     
         48 . An anesthetic delivery system according to  claim 38 , wherein the control algorithm includes a top-up algorithm for setting the rate of flow of anesthetic liquid from the liquid pump to the vaporizer, the top-up algorithm derived from the mathematical relationship:
   ( FwA−FcA )* Vt* 60/( Tb*K )   wherein:   FwA is the selected concentration of anesthetic in the inspired air;   FcA is the measured concentration of gaseous anesthetic;   Vt is a tidal volume of air delivered by the ventilator;   Tb is the breath period; and   K is a constant comprising a ratio of gas volume to liquid volume for the specific anesthetic used in the method.   
     
     
         49 . An anesthetic delivery system according to  claim 38 , wherein the control algorithm includes a top-up algorithm for setting the rate of flow of anesthetic liquid from the liquid pump to the vaporizer, the top-up algorithm derived from the mathematical relationship:
   ( FwA−FmA )* Vt* 60/( Tb*K )+via Ln− 1   wherein:   FwA is a selected concentration of anesthetic in the inspired air;   FmA is an actual concentration of incoming anesthetic at the subject's airway;   Vt is a tidal volume of air delivered by the ventilator;   Tb is a period of the subject's breath;   K is a constant comprising a ratio of gas volume to liquid volume for the specific anesthetic used in the method; and   viaLn−1 is the rate of flow of the liquid pump in the previous breath.   
     
     
         50 . An anesthetic delivery system according to  claim 38 , comprising a pressure transducer for determining the beginning and end of an inspiratory cycle. 
     
     
         51 . An anesthetic delivery system according to  claim 38 , comprising conduits ( 33 ,  37 ) that provide pathways for a gas flow between the inspiration limb ( 19   i ) and the anesthetic delivery device ( 20 ), wherein the homogenizer ( 39 ) and the conduits ( 33 , 37 ) provide a bias flow to the anesthetic vapor being generated in the anesthetic delivery device ( 20 ), and wherein the homogenizer ( 39 ) stores the bias flow enriched with anesthetic vapor during exhalation until the next inhalation. 
     
     
         52 . An anesthetic delivery system according to  claim 38 , comprising an inspiratory tube ( 19 ) of the inspiratory limb ( 19   i ), the flow sensor ( 44 ) and the anesthetic analyzer ( 46 ) connected to the inspiratory tube ( 19 ) between the anesthetic inlet port and the ventilator.